High-water-dispersible calcite pigment



Patented Mar. 19, 1946 UNITED STATES PATENT OFFICE HIGH-WATER-DIS PIG PERSIBLE CALCITE MENT Kenneth S. Mowlds, Baltimore, Md., assignor to The Glidden Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application May 23, 1942,

' Serial No. 444,258

. 2 Claims. (Cl. 106124) This application is a continuation-in-part of my application Serial No. 350,058, filed August 2, 1940.

This invention relates to aqueous dispersions of light-weight pigments comprising calcium carbonate and has particular reference to aqueous dispersions of these pigments wherein the concentrations of the light-weight pigments are un- 7 usually high.

Among the objects of this invention is the preparation of aqueous dispersions of light-weight.

pigments comprising calcium carbonate of sufficient concentration of pigment to give the desired covering and hiding powers when these aqueousdispersions are employed as coating compositions and the like.

Another object of this invention is the repaparticularly desirable in aqueous coating compositions; especially, if it possesses covering power equal to or substantially equal to that of calcium sulfate, since calcite unlike calcium sulfate pigment can be mixed or slurried with water.

According to a specific embodiment of the present invention a method is provided whereby a ration of aqueousgdispersions'of light-weight pigments comprising calcium carbonate of concentrations highly in excess of the. concentrations of pigments in normalaqueous dispersions of'such igments of corresponding viscosity and .consistency; that is, from 2 to 5 timesas much pigment as is contained in normal aqueous dispersi ns of such pigments of corresponding viscosityand consistency.

A'further object of this invention is ,the' prepacalcium carbonate'in' asimple,highly efficientand inexpensive manner.;.'

1 A further object of thisinvention is'tlie preparationof aqueous dispersions oi -high concentrationof calcium carbonate pigment; the calcium.

carbonate particles being in less reactive-condirationjof 'these aqueousdispersions of high con-f w centration of light-weight:pigments comprising calcite dispersion is prepared of high concentra- 1 tion and which has a covering power equal to or f substantially equal to that of calcium sulfate.'-- The dispersion produced'has excellent working f properties, the working properties being similar to those of clay. The dispersiqmis continuously flowing, has a high igment concentration at working consistency,;and possesses high covering and.hiding-power. The dispersion may be used in various .ways

1 such, as in "water paints, inwallpaper andother papers. The dispersions prepared according-"to the present inventionmay also be used'withrprm" tein binders'such as casein-and soyibean'protein. Such combinations may 'be' readily used in the tion and thus less prone to discoloration when-. t.

employed with binders, such colorationland darkening.

A still further object of this invention is "the preparation of these aqueous dispersions. of high I p as the amines or proteins which have a tendency topromote disconcentration of light-weight pigmentsina form whereinthe pigment will persist in dispersed state for an extraordinary length of time.

Other, further andmore specific objects of this invention will become readily apparent to persons skilled in the art from a consideration of the following description:

Calcium carbonate, such as calcite, narily dispersible in water to any great extent.

a If an attempt is made to prepare an aqueous'dis-- persion of calcite, a thick pastforms with relatively small concentration of calcite.- Thus, when 1200 grams of ground calcite per liter are dispersed in water, a thick paste is formed. This 55 preparations of water panda-paper; coatings and sizing compositions.

In" accordance with the -present invention a water soluble phosphateiis used to improve the dispersion. Anysoluble phosphate may: be'used,

such as trisodium phosphate, sodium tetra phosphate, tetra sodium pyrophosphate, etc. The pyrophosphates are preferred. The amount of phosphate may vary from 0.1% to 5%, more or less, based.v on the calcite present, although in some cases more maybe desired if soluble alkaline is not drdiearth compounds are present. f The soluble alkaline earth compounds readily react with the phosphate and form insoluble alkaline earth phosphates. These precipitated alkaline earth phosphates coat the finely divided calcium carbonate particles, making the latter less reactive. When this less reactive pigmentis employed in certain coating -compositions, such as those employing amine or protein binders, the tendency toward precipitation of the binders is considerably reduced. In treating calcite, there shouldbe sufllcient soluble phosphate left alter precipitation of alkaline'earth phosphates to effect the desired dispersion of the calcite or similar pigment. This dispersing action of soluble phosphates may be used either to effect a higher concentration of calcite, or to control the viscosity of the disper. sion, or both. For example, if 0.3% of Na4Pi01 be used, 2500 grams of calcite per liter may be dispersed'in water to give a thin slurry which flows like water.

The calcium carbonate or calcite treated according to my invention is particularly adapted for use with amine and protein binders. In prior processes, when calcite is employed with amine and protein binders, the extraneous water-soluble alkaline earth substances (which generally vary from 0.01 to 0.1%) react with the amine and protein binders, forming insoluble reaction products and thus "kicking or precipitating these binders out of solution to the extent of the amount of Water-soluble alkaline earth substances present.

My process eliminates this kicking efiect and is, therefore, highly advantageous because precipitation of the binders results in:

(1) Reduction of adhesiveness of coating to the surface applied.

(2) Marked increase in the viscosity of the aqueous dispersion.

(3) Production of coarser texture of film.

The following specific examples will illustrate the practice of my invention:

Example I To 100 grams of calcite there is added 0.3 gram of sodium pyrophosphate. The mixture is ground togetherin. dry form and then introduced into about 30-35 cubic centimeters of water, forming a slurry or semi-paste.

The composition, prepared as above, gives excellent covering when used in coating wallpaper. Attempts to make a satisfactory coating for wallpaper withcalcite, but without using the phosphates, have been found unsatisfactory due to the low pigment concentration and high viscosity of the attempted dispersions.

' My composition, as above prepared, may be used advantageously with gelatinous binders, such as alginates, glue, casein and vegetable protein. It works well with vegetable protein derived from soy bean.

Example II the sodium and Another use of the calcite dispersions of the present invention is in the preparation or coni-- posite pigments containing calcite, such as a Tim-calcite composite pigment. The procedure in such a case may be to first prepare a thin dispersion of calcite in accordance with the present invention, and effect a hydro-separation of the dispersion. The eilluent containing the fines may then be mixed with a TiOz slurry and the mixture coagulated with a water-soluble alkaline earth salt or other coagulating agent, and the coagulated composite separated from the water. Also, dispersions of calcite and other CaCOa pigment prepared according to my invention, may be used with pigments other than TiOz in the preparation of composite pigments. Examples of such other pigments used in lieu of TiOz are .ZnS, cadmium yellows and reds, chromates, iron blues, iron reds, iron yellows and organic pigments.

The expression normal aqueous dispersions as employed in the claims is intended to be construed as dispersions in water which contains no dissolved substance.

The present invention is not limited to the specific details set forth in the foregoing examples which should be construed as illustrative and not by way of limitation, in of the numerous modifications which may be eiiected therein without departing from the spirit and scope of this invention, it is desired that only such limitations be imposed as are indicated in the appended claims.

I claim as my invention:

1. A composition of matter comprising a highly persistent aqueous dispersion of calcite pigment coated with alkaline earth phosphate material and having a concentration of pigment at least twice as great as the c'oncentration'of such pigment in normal aqueous dispersions of such pigment of corresponding viscosity, said dispersion having in solution 0.1 to 5% of a Water-soluble pyrophosphate of an alkali metal based on the amount of pigment, the'pyrophosphate of alkali metal being sufiicient to precipitate all soluble alkaline earth. compounds in the calcite and for effecting the dispersion of the coated calcite.

2. A composition of matter comprising a protein and a highly persistent aqueous dispersion of calcite pigment coated with alkaline earth phosphate material and having a concentration of pigment at least twice as great as the concentration of such pigment in normal aqueous dispersions of such pigment of corresponding viscosity, said dispersion having in solution 0.1 to 5% of a water-soluble,pyrophosphate of an alkali metal based on the amount of pigment, the pyrophosphate of alkali metal being suiiicient to precipitate all soluble alkaline earth compounds in the calcite. and for effecting the dispersion of the coated calcite.

' KENNETH S. MOWLDS. 

